“Hands down the loftiest 15°F bag I’ve ever used,” declared our tester after using the Xenon on a September hike in Colorado’s Flat Tops Wilderness, where her companion grumbled, “It practically fills the tent.” Credit the 850-fill goose down—and lots of it: Marmot crams 20 to 25 percent more down into this women’s model than a comparably rated men’s bag (because many women sleep colder than guys). Much of that extra insulation gets loaded into horizontal baffles at the core and foot, which helps this bag deliver on its 15°F promise: On a 20°F night camped on alpine tundra, our tester never even felt the chill. The comfort-cut mummy is wide through the shoulders and hips (our curviest testers called it “efficient but unrestrictive”), yet tapers sharply at the foot to reduce dead air space around cold-prone toes.